1. Field of the Invention
The present invention relates to a mold used during the drilling of through-holes or the like or during the cutting of a large printed wiring board which has printed wiring circuits provided theron into a plurality of printed wiring boards.
2. Description of the Related Art
A printed wiring board is generally manufactured by subjecting a copper clad laminate to a series of treatments, such as etching, applying a solder resist, printing a shield layer, printing an overcoat layer, etc.
A mold for a printed wiring board is used in the process of drilling through-holes in the printed wiring board or in the process of cutting a large board having a plurality of printed wiring circuits provided thereon into a plurality of respective printed wiring boards.
FIGS. 7(a) and 7(b) show a conventional mold for use during a process of drilling through-holes or the like. The mold comprises a lower die 72 secured to a base 71 and an upper die 73 arranged to move up and down against the lower die 72 and operative so as to sandwich the printed wiring board (not shown) between it and the lower die 72. The upper die 73 is provided at the positions corresponding to where it is intended to drill the through-holes. The upper die 73 has a plurality of holes, through which punching pins 74 pass up and down during drilling. The lower die 72 is provided, at positions corresponding to respective punching pins 74, with punching holes 75, through which the punching pins 74 are inserted. The upper and lower dies 73,72 have flat press surfaces for sandwiching and fixing the printed board therebetween.
Initially, the printed wiring board, comprising only a base material, has a flat surface. However, at a later stage of manufacture, the board has an uneven surface, that is, it contains concave and convex regions, since the printed wiring circuit is formed on the base material by the above-mentioned series of treatments. Moreover, the depth of the concave and convex surface regions becomes large as the circuit construction becomes more complicated.
FIG. 8 shows a cross-section of a jumper circuit portion of a printed wiring board 1, in which an electrical circuit 3 and connecting lands 4 are provided on a base material 2. A solder resist 5 is applied on the circuit 3 and connecting lands 4. A jumper circuit 6 serves to electrically connect the connecting lands 4 located on both sides of the circuit 3. The jumper circuit is formed by printing a conductive ink along the exposed connecting land 4. An insulating overcoat 7 is applied on the jumper circuit 6, thereby forming the printed circuit board 1. The portion of the printed wiring board containing the jumper circuit 6 contains a step with a thickness which is physically greater than that of other regions of the printed wiring board. The thickness of the step is on the order of 0.1 mm, thereby presenting concave and convex regions on the surface of the printed wiring board.
If the printed wiring board containing a printed wiring circuit is sandwiched between the upper and lower dies of the conventional mold, a clearance or gap is formed between the flat press surface of the mold and the low level, or concave, portions of the printed wiring board, i.e., those portions containing no printed circuit elements. The mold thus cannot be pressed evenly over the whole surface of the printed wiring board, and thus, problems arise. For example, when drilling holes, the diameter of the holes changes and the hole becomes slanted. When cutting, a dimensional error arises. Moreover, the pressing force becomes uneven, resulting in deformation and cracking of the printed wiring board, accidental cutting of the printed wiring circuit, and injury to the press surface of the mold.